Are you on the pill now? Or are you wanting to start the pill right away, to see if you can stop your period from coming?
Why do you say there is a 50/50 chance you are pregnant?
I tried to delay my period with birth control after I had already been on it for a couple months. Didn't work at all - I ended up having my period for the entire month including the time I wanted it to be gone.
Don't take birth control if you're pregnant!!